Project Summary/Abstract While smoking prevalence stagnates in the U.S., novel tobacco products like electronic cigarettes (ECIGs) are gaining popularity among adults, adolescents, and never smokers. ECIGs use a battery-powered heating element to aerosolize a liquid that often contains the dependence-producing drug nicotine. Nicotine delivery and the dependence potential of these products may be influenced by ECIG device features that are largely under the control of the user (e.g., liquid nicotine concentration and heating element resistance). Of particular concern is the proliferation of ECIG devices with low resistance heating elements (measured in Ohms, ?) that are <1?. ECIG users, refer to these <1? devices as ?sub-Ohm? ECIGs. Preliminary data reveal that ECIGs with <1? resistance heaters may deliver nicotine effectively, despite often being paired with low liquid nicotine concentrations. However, the extent to which decreasing ECIG heater resistance influences nicotine delivery and user subjective experience, two factors predictive of dependence, remains unclear. In addition, the beliefs and harm perceptions held by ECIG users who prefer ?sub-Ohm? ECIGs remains unexplored and is relevant to predicting uptake and continued use of these devices. Understanding nicotine delivery, subjective experience and the beliefs and harm perceptions held by those ECIG users who prefer ?sub-Ohm? ECIGs will be paramount to protecting individual and public health. Therefore, this proposal describes two primary aims. Aim 1 will measure the effect of <1? heater resistance and liquid nicotine concentration on nicotine delivery and user subjective effects. This 2 (heater resistance) by 2 (nicotine concentration) within-subject human/clinical laboratory design will elucidate the individual and combined effects of these factors on plasma nicotine concentration and subjective effects in 32 experienced ECIG users. Aim 2 will use a mixed-method participatory research exercise called concept mapping to characterize the beliefs, health/dependence perceptions, and perceived effects driving ?sub-Ohm? ECIG use. The hypotheses of these two aims are: 1) ECIGs with <1??heater resistance will result in greater nicotine delivery and will be associated with more positive subjective effect profiles, suggestive of higher dependence potential and 2) ?sub-Ohm? ECIGs will be associated with favorable beliefs and positive perceived effects of use, as well as less risk of harm and nicotine dependence, making their use more likely. Results from this project will result in further understanding of factors that can influence ECIG dependence potential and reasons driving the use of ?sub-Ohm? ECIGs, likely informing regulation of this novel tobacco product category, while also providing an unparalleled training experience.